1. Technical Field
The present invention relates to a position indicator of an electromagnetic induction system and an electronic ink cartridge housed in the position indicator of the electromagnetic induction system.
2. Description of the Related Art
As disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2002-244806), for example, a coordinate input device of an electromagnetic induction system includes: a position detecting device having a sensor formed by disposing a large number of loop coils in the direction of an X-axis as a coordinate axis and the direction of a Y-axis as a coordinate axis; and a position indicator in the shape of a pen, the position indicator having a resonance circuit including a coil as an example of an inductance element wound around a magnetic core and a capacitor.
The position detecting device supplies a transmission signal of a predetermined frequency to a loop coil of the sensor. The loop coil transmits the transmission signal as electromagnetic energy to the position indicator. The resonance circuit of the position indicator is configured to have a resonance frequency according to the frequency of the transmission signal. The resonance circuit stores the electromagnetic energy on the basis of electromagnetic induction action between the resonance circuit and the loop coil of the sensor. Then, the position indicator returns the electromagnetic energy stored in the resonance circuit to a loop coil of the sensor of the position detecting device.
The loop coil of the sensor detects the electromagnetic energy from the position indicator. The position detecting device detects the coordinate values in the X-axis direction and the Y-axis direction of a position indicated by the position indicator on the sensor on the basis of the position of the loop coil that supplied the transmission signal and the position of the loop coil that detected the electromagnetic energy from the resonance circuit of the position indicator.
A position indicator of this kind has a constitution for transmitting a force applied to the core body of the position indicator in the shape of a pen, that is, pen pressure, as a change in resonance frequency (or phase) of a resonance circuit to a position detecting device, so that the position detecting device can detect the pen pressure. A constitution that changes the capacitance of a capacitor forming the resonance circuit is known as an example of the constitution that changes the resonance frequency of the resonance circuit according to the pen pressure.
A position indicator using a variable capacitance type capacitor as described in Patent Document 2 (Japanese Patent Laid-Open No. Hei 4-96212), for example, is known as a conventional position indicator that detects pen pressure on the basis of a change in capacitance of a capacitor forming a resonance circuit. The variable capacitance type capacitor described in this Patent Document 2 includes, as mechanical structural parts housed within a cylindrical casing, a first conductor attached to one end surface of a cylindrical dielectric and a flexible second conductor capable of elastic displacement, the flexible second conductor being disposed on another end surface side of the dielectric, the another end surface side being opposite from the one end surface of the dielectric. A surface of the second conductor which surface is opposed to the dielectric has such a shape as to swell on the side of the dielectric in the form of a dome, for example.
The variable capacitance type capacitor described in Patent Document 2 also includes spacer means for separating the second conductor and the another end surface of the dielectric from each other by a small interval except for a part of the second conductor and the another end surface of the dielectric, and further includes a part for applying a relative pressure or displacement between the second conductor and the dielectric. The part for applying the relative pressure or displacement is coupled to a core body of the position indicator in the shape of a pen. When a pen pressure is applied to the position indicator from one end part of the casing of the position indicator, the force in an axial direction which force is applied to the core body displaces the flexible second conductor to the dielectric side, and thus displaces the second conductor so as to touch the another end surface of the dielectric. Then, the swelling end surface of the flexible second conductor which swelling end surface is in the shape of a dome touches the another end surface of the dielectric with an area corresponding to the pressing force. Therefore a capacitance formed between the second conductor and the first conductor with the dielectric interposed therebetween changes.